Corn contains about 20% w/v of proteins, branched-chain amino acids (BCAA) of which 20-30% w/v based on the proteins. Corn gluten is obtained as a product in the process of isolating sugar components from corn and preparing cornstarch and corn dextrin. In corn gluten, BCAA are included with a content of 20-30 weight %, based on proteins which are included in about 60% w/v.
However, BCAA (leucine, isoleucine and valine) content in the final corn gluten hydrolysate is even lower because of the variation of isoelectric point of the amino acids and the precipitation and breakdown of amino acids caused by chemical and physical factors during the process of producing a hydrolysate from a plant protein-containing raw material including corn gluten. Further, if the content of free amino acids eluted in aqueous solution becomes lower because of low availability of the proteins included in the raw material, BCAA (leucine, isoleucine and valine) content in the final corn gluten hydrolysate becomes even lower.
In addition to the low BCAA content problem in hydrolysis, loss of free amino acids in the following process of treating the aqueous hydrolysate solution may be a problem. In particular, activated carbon usually used for decolorization and deodorization of protein hydrolysate may result in adsorption of large-molecular-weight peptides and proteins, thereby leading to decreased contents of TN, AN (amino nitrogen) and free amino acids including BCAA.
As described above, there exist various factors resulting in the decrease of free amino acid content in the procedures from the preparation of corn gluten hydrolysate to hydrolysis and treatment of the hydrolysate. As a result, the BCAA (leucine, isoleucine and valine) content of the hydrolysate is lower than that of the raw material. Accordingly, in order to increase free amino acid content and BCAA content of the final product, improved pre-treatment and concentration processes of BCAA content of corn gluten are required.